Plotting problem
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Hi. I've written this code to plot the graph it produces. However, the top three lines have complex parts to them. How can I plot only the real parts? Code follows:
%Matlab code for "MATLAB
%Question 1
%
%13/02/12
function [lmda, Ct] = problem
%QUESTION 1%
rs=0.05; %rotor solidity
Cl=2*pi; %specific lift coefficient
pa1=0.1745329250; %pitch angle 1
pa2=0.0872664625; %pitch angle 2
pa3=-0.0017453292; %pitch angle 3
pa4=-0.0349065850; %pitch angle 4
pa5=-0.0872664625; %pitch angle 5
%--------------------%
i=1;
for lmda=0:0.1:20;
a2(i)=(((((rs*lmda*Cl)/16)+0.5)^2)-((rs*lmda*Cl*(1-(lmda*pa1)))/8));
if a2(i) < 0
break
end
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
a1(i)=(((rs*lmda*Cl)/16)+0.5);
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
at(i)=a1(i)-sqrt(a2(i));
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
Ct1(i)=((rs*(lmda^2)*Cl)/2)*(((1-at(i))/lmda)-pa1);
i=i+1;
end
%----------------------------------------------------------------%
i=1;
for lmda=0:0.1:20;
a2(i)=(((((rs*lmda*Cl)/16)+0.5)^2)-((rs*lmda*Cl*(1-(lmda*pa2)))/8));
if a2(i) < 0
break
end
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
a1(i)=(((rs*lmda*Cl)/16)+0.5);
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
at(i)=a1(i)-sqrt(a2(i));
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
Ct2(i)=((rs*(lmda^2)*Cl)/2)*(((1-at(i))/lmda)-pa2);
i=i+1;
end
%----------------------------------------------------------------%
i=1;
for lmda=0:0.1:20;
a2(i)=(((((rs*lmda*Cl)/16)+0.5)^2)-((rs*lmda*Cl*(1-(lmda*pa3)))/8));
if a2(i) < 0
break
end
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
a1(i)=(((rs*lmda*Cl)/16)+0.5);
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
at(i)=a1(i)-sqrt(a2(i));
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
Ct3(i)=((rs*(lmda^2)*Cl)/2)*(((1-at(i))/lmda)-pa3);
i=i+1;
end
%----------------------------------------------------------------%
i=1;
for lmda=0:0.1:20;
a2(i)=(((((rs*lmda*Cl)/16)+0.5)^2)-((rs*lmda*Cl*(1-(lmda*pa4)))/8));
if a2(i) < 0
break
end
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
a1(i)=(((rs*lmda*Cl)/16)+0.5);
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
at(i)=a1(i)-sqrt(a2(i));
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
Ct4(i)=((rs*(lmda^2)*Cl)/2)*(((1-at(i))/lmda)-pa4);
i=i+1;
end
%----------------------------------------------------------------%
i=1;
for lmda=0:0.1:20;
a2(i)=(((((rs*lmda*Cl)/16)+0.5)^2)-((rs*lmda*Cl*(1-(lmda*pa5)))/8));
if a2(i) < 0
break
end
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
a1(i)=(((rs*lmda*Cl)/16)+0.5);
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
at(i)=a1(i)-sqrt(a2(i));
i=i+1;
end
%--------------------%
i=1;
for lmda=(0:0.1:20);
Ct5(i)=((rs*(lmda^2)*Cl)/2)*(((1-at(i))/lmda)-pa5);
i=i+1;
end
%----------------------------------------------------------------%
lmda=(0:0.1:20);
figure,plot(lmda,real(Ct1),'k-','Linewidth',2),grid on, hold on
plot(lmda,real(Ct2),'k--','Linewidth',2)
plot(lmda,real(Ct3),'k-.','Linewidth',2)
plot(lmda,real(Ct4),'r-','Linewidth',2)
plot(lmda,real(Ct5),'r--','Linewidth',2)
axis([0 20 0 1])
xlabel('\lambda');ylabel('C_t');title('Thrust coefficient against tip speed ratio.');
legend('\theta_T=10^{o}','\theta_T=5^{o}','\theta_T=-0.1^{o}','\theta_T=-2^{o}','\theta_T=-5^{o}');
end
%QUESTION 2%
0 commentaires
Réponse acceptée
Matt Tearle
le 22 Fév 2012
You are plotting only the real parts. I think the problem is coming with how you're calculating these functions. You have break statements to terminate your for loops when a2 goes negative. However, the last value of a2 (the negative value) is still there.
Furthermore, you're reusing a2, but you stop calculating after a2 goes negative. This means that the rest of a2 is still there from the previous calculation. Do you really want that?
If you zoom out, so the y-axis goes higher, you will see that the function carries on doing something else. My suspicion is that this comes from calculating at based on old a2 values.
Finally, you really don't need these loops. This code is really nasty to read and debug.
lmda=0:0.1:20;
a1=(((rs*lmda*Cl)/16)+0.5);
Nice and easy. Just remember to use .* and ./ when multiplying/dividing arrays.
Plus de réponses (2)
J
le 22 Fév 2012
3 commentaires
Matt Tearle
le 24 Fév 2012
Because MathWorks pays more :)
Maybe some of these suggestions might help you:
http://www.mathworks.com/matlabcentral/answers/8026-best-way-s-to-master-matlab
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